The present invention relates to an electric compressor driven by an electric motor.
Japanese Unexamined Patent Publication No. 5-187356 discloses an electric compressor, the rotary shaft of which is driven by an electric motor. The compressor has several cylinder bores. A piston is accommodated in each cylinder bore. The pistons are arranged at equal angular intervals about the axis of the rotary shaft. A drive plate is fixed to the rotary shaft. A swash plate and a piston support are located between the drive plate and the pistons. The piston support is supported by a thrust bearing. The thrust bearing permits the piston support to rotate relative to the swash plate.
A guide groove is formed in the drive plate. A pivot pin, which is fixed to the swash plate, is engaged with the guide groove. A sleeve is slidably supported by the rotary shaft. The swash plate is supported by a pair of sleeve pins, which are formed on the sleeve, such that the swash plate inclines. Inclination of the swash plate is guided by engagement between the guide groove and the pivot pin and sliding of the sleeve. As the swash plate rotates, the piston support pivots and reciprocates each piston in the corresponding cylinder bore. When gas is compressed in each cylinder bore and is discharged from the cylinder bore, a compression reaction force is generated. The compression reaction force is transmitted to and received by the drive plate through the pistons, the piston support, the thrust bearing, the swash plate and the pivot pin.
The compression reaction force applies load torque on the rotary shaft. The load torque generated by each piston is maximized during the discharge stroke, in which gas is discharged from the cylinder bore. The load torque is substantially zero during the suction stroke, in which gas is drawn into the cylinder bore. The net load torques of the pistons is maximized a number of times that correspond to the number of the pistons during one turn of the rotary shaft.
The driving torque generated by the rotary shaft is always greater than the maximum value of the net load torque. The driving torque is determined by taking only the maximum value of the net load torque generated by the compression reaction force into account. Since changes of the net load torque are not considered, the driving torque is excessive when the net load torque has a small value. Thus, an electric motor that generates excessive torque is used. The motor, which generates excessive torque, is relatively large, which increases the size of the compressor.
Accordingly, it is an objective of the present invention to provide a compact electric compressor.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, an electric compressor is provided. The electric compressor includes an electric motor that generates driving torque, a rotary shaft driven by the motor and a compression member for compressing gas in accordance with rotation of the rotary shaft. During one turn of the rotary shaft, at least one time when the net load torque generated in the compression member is minimum and one time when the driving torque of the motor is minimum occur at substantially the same rotation angle of the rotary shaft or at least one time when the net load torque is maximum and one time when the driving torque of the motor is maximum occur at substantially the same rotation angle of the rotary shaft. The magnitude of the driving torque is always greater than that of the net torque.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.